Secondary recovery process utilizing brine electrolyzed to remove hydrogen sulfide

ABSTRACT

A process for the recovery of liquid hydrocarbons in which brine is injected into the formation via an injection well and a mixture of liquid hydrocarbons together with brine contaminated with hydrogen sulfide is recovered through a production well. After separation of the liquid hydrocarbons, the brine is subjected to electrolysis to form sodium hypochlorite which reacts with the hydrogen sulfide to yield brine having a substantially reduced hydrogen sulfide content suitable for reinjection into the formation.

United States Patent Schievelbein et al. Jan. 8, 1974 SECONDARY RECOVERY PROCESS 2,786,529 3/1957 Parsons l66/266 UTILIZING BRINE ELECTROLYZED T0 REMOVE HYDROGEN SULFIDE 332741101 9/1966 West et a1 .1 166/266 x Inventors: Vernon I-l. Schievelbein; Leonard A.

Shankle, both of Houston, Tex.; Herbert N. Wade, Riverside, Conn.

Primary Examiner-Stephen J. Novosad Attorney-Thomas l-l. Whaley et al.

[73] Assignee: Texaco Inc., New York, NY.

[22] Filed: Jan. 7, 1972 [57] ABSTRACT [2]] App]. No.: 216,190 process for the recovery of liquid hydrocarbons in which brine is injected into the formation via an injection well and a mixture of liquid hydrocarbons to- C(il. gather with brine contaminated with hydrogen sulfide [58] Fieid 267 is recovered through a production well. After separa- 6 tion of the liquid hydrocarbons, the brine is subjected v to electrolysis to form sodium hypochlorite which re- [56] References Cited acts with the hydrogen sulfide to yield brine having a substantially reduced hydrogen sulfide content suit- UNITED STATES PATENTS able for reinjection into the formation. 2,370,507 2/1945 Teichmann et al. 166/266 v I 2,720,265 10/1955 Tracht 166/266 2 Claims, 2 Drawing Figures SEA/4mm? l i l [f Z4 Eff/(LE St'l'iZ/NG 55/72 we 7Z/YK BAS/N 545/0 /6 /'Zfl I 07/ /V 7 7NK /7 CELL F/L 7E? #90 /'/9b a an ac POM/E? -/9 swea -5 SOURCE 77I/V/i 32 H/fl/ PFfSIflIEpJ/ /P Z5 SECONDARY RECOVERY PROCESS UTILIZING BRINE ELECTROLYZED TO REMOVE HYDROGEN SULFIDE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the secondary recovery of liquid hydrocarbons from subterranean formations. In particular, this invention relates to a water flooding process in which brine recovered with the oil is electrolyzed to reduce the hydrogen sulfide content thereof.

2. Description of the Prior Art The presence of hydrogen sulfide in brine which must be handled in the course of a variety of oil-field and refinery operations often gives rise to costly and serious problems. Such water is extremely corrosive to metal equipment and when exposed to air, hydrogen sulfide liberated from the sour brine may pollute the air to the extent that damage to equipment and building may occur and may be incompatible with plant and animal life.

Many of the processes which have been developed and operated commercially for removal of hydrogen sulfide from sour brines have often resulted in pollution of the air. These include aeration of water where large quantities of hydrogen sulfide are allowed to escape into the air; bubbling exhaust gas through the sour brine water (stripping) and allowing hydrogen sulfide to escape into the air with the exhaust gas; bubbling air through sour brine, trapping the air containing the hydrogen sulfide and burning to odorless but just as hazardous sulfur dioxide; stripping with hydrocarbon gas or gases and burning the sulfur dioxide in air, etc. All of these procedures can be employed to effectively remove hydrogen sulfide from sour brine but in each instance substantial air pollution results.

Stripping of hydrogen sulfide from brine without pollution of air is possible if an inert gas such as natural gas or nitrogen is utilized as a stripping gas and the hydrogen sulfide removed is recovered from the stripping gas by physical or chemical processes known to the natural gas industry (i.e. MEA (monoethanolamine), DEA (diethanolamine), Giammarco, Vetrocoke, Thylox, Ferox, and Manchester processes or by using sodium carbonate, sodium hydroxide, lime or iron solutions. Although these procedures are very effective for removal of the hydrogen sulfide in such a way that no air pollution results, the chemicals, equipment and operating costs are very high with the result that they are not always economically feasible.

It is possible through the addition of chemicals to sour brine to control the hydrogen sulfide content thereof to some degree. For example, the addition of sufficient caustic to maintain the pH of the brine at 8.5 or higher will prevent the escape of hydrogen sulfide but the cost of such an operation is generally prohibitive because of the quantity of caustic required. Chlorine or sulfur dioxide may also be used for hydrogen sulfide control but these gases are expensive, dangerous and difficult to handle.

There is need in the art, therefore, for an efficient, economical process for removal of hydrogen sulfide from brine in which pollution of the atmosphere with the undesirable hydrogen sulfide and associated offgases is avoided.

SUMMARY OF THE INVENTION In its broadest aspect, this invention relates to a process for treating hydrogen sulfide contaminated sour brine by electrolysis to form sodium hypochlorite whereby reaction with the hydrogen sulfide yields brine with a reduced sulfide content. In another aspect, this invention relates to a secondary recovery process wherein hydrogen sulfide containing brine produced simultaneously with the oil is treated as described above to reduce the hydrogen sulfide concentration ans the thus-treated brine is reinjected into the formation.

In the drawings:

FIG. I is a flow diagram of one preferred embodiment of the invention; and

FIG. 2 is a schematic illustration of a second embodiment of the invention in which the electrolysis cell is shown partly in section.

DETAILED DESCRIPTION OF THE INVENTION The process of this invention in which fluid hydrocarbons are recovered from a subterranean formation penetrated by an injection well and a production well, comprises:

a. injecting brine into said formation through the injection well,

b. forcing the said brine toward said production well,

c. withdrawing a mixture of the liquid hydrocarbon and brine containing hydrogen sulfide from said production well,

d. separating said liquid hydrocarbon from the hydrogen sulfide containing brine,

e. subjecting the hydrogen sulfide containing brine to electrolysis to form sodium hypochlorite whereb reaction with the said hydrogen sulfide yields brine with a substantially reduced hydrogen sulfide content,

f. separating insolubles from the treated brine, and

g. reinjecting the thus-treated brine into the said injection well.

For a more complete understanding of the process, reference is made to FIG. 1 which depicts one embodiment of the invention.

A mixture of sour brine and oil, i.e., contaminated with hydrogen sulfide, from a production well in an oil field being produced by a secondary recovery process utilizing a water flood enters the treatment system via line 10 and is passed to oil separator 11, which can be a decanter or a decanter followed by an oil skimming device, from which oil is removed by means of line 12 and is sent to storage as production oil. Leaving separa tor 11 and sour brine passes by means of line 13 to encloded recycle tank 14. Sour brine is withdrawn from recycle tank 14 by means of line 15 and transmitted by means of pump 16 into a closed electrolysis cell 18 via line 17. Direct current power source 19 is connected to the electrodes of electrolysis cell 18 by means of conductors 19a and 19b. Any of a number of hypochlorite cells known in the art may be utilized in the electrolysis cell section of this process. Treated brine containing (1) electrolysis products including sodium hydroxide, chlorine and hydrogen, (2) sodium hypochlorite formed in the cell by reaction of chlorine and sodium hydroxide and (3) sulfur and sulfate ions (usually as sodium sulfate) formed by reaction of sodium hypochlorite and hydrogen sulfide together with unreacted hydrogen sulfide are withdrawn from the electrolysis cell 18 and passed to recycle tank 14 by means of line 20.

Hydrogen off-gas from the formation of the sodium hydroxide in the cell is vented from line 20 to an appropriate disposal system via line 21. Treated brine from recycle tank 14 is sent by means of line 22 to settling basin 23 and then via line 24 to second settling basin 25. In settling tanks 23 and 25 solid materials, such as sulfur and any other insolubles present in the brine are permitted to settle out of the treated brine. From basin 25 the treated brine is conducted to agitated mixing tank 27 by line 26. Alum as a flocculent is added to the brine in mixing tank 27. Treated brine is withdrawn via line 28 and sent to sand filter 29 for removal of remaining suspended solids. Discharged treated brine from sand filter 29 is passed by line 30 to surge tank 31 and then into the inlet side of high pressure pump 33 via line 32. Output from high pressure pump 33 is conducted via line 34 to the injection wells in the field for reinjection to the producing formation.

During the electrolysis step at the anode chlorine will be produced:

2 Cl' Cl +2e 1 and at the cathode, hydroxide ions will form:

2e 2 H O H 2 OH 2 In the hypochlorite cell utilized, the brine flows through the electrodes at such a rate that the electroly' sis products are comingled as they are rapidly swept away from the electrodes and under these conditions the chlorine generated will combine with the hydroxide according to the reaction:

C1 2 OH"- Cl ClO+ H 3 The hypochlorite ion (ClO') will then react with the H 8 according to the following reactions:

H S OCF S H O Cl" 4 20H H S 4 OCl- S0 4 Cl 2 11 0 Thus, through electrolysis, the hydrogen sulfide is converted to non-toxic, non-corrosive and insoluble sulfur and to water-soluble non-toxic and unvaporizable sulfate ion.

The temperature at which the sour brine is electrolyzed in the cell is not critical and generally will vary from about to about 45C. The concentration of the hydrogen sulfide in the sour brine will vary over wide limits although generally it will be from about 2 to about 500 ppm.

As previously pointed out, this invention is not limited to the use of any particular type of hypochlorite cell. The cell shown in FIG. 2 has been successfully employed in reducing the hydrogen sulfide content of sour brine. The body 61 of the cell was a 5 /2 I.D. steel pipe 120 inches in length capped at one end. This section of pipe constituted the cathode of the cell and was con nected at 62 to he negative side ofa DC power source 63 by conductor 62a.

The positive side of this power source was connected through ammeter 64 to the positive connection 65 of the cell which was a cylindrical galvanized iron rod about inch by 18 inches installed in a longitudinal position along the centerline and in direct electrical contact with the anode 66. Ammeter 64 was connected to positive connection 65 by conductor 64b and to power source 63 by conductor 64c. Voltmeter 640 was connected between cell body 61 at 62 by conductor 62b and to the positive cell connection 65 by conductor 64e. Anode 66, which was a graphite rod (3 inches CD. by 60 inches in length) mounted concentrically inside the cell body and extending about 4 inches beyond the end of cell body 61, was insulated from it by insulating supports 67. Insulating support 670 served to form a water-tight closure at the end of the cell between the anode 66 and the cell body 61. Sour brine is introduced into the cell via non-conducting feed line 68 and after passing through the concentric annular space between cell body 61 and anode 66 is removed from the cell via non-conducting line 69. Lines 68 and 69 were fabricated from polyvinylchloride tubing.

EXAMPLE I Using the cell of FIG. 2, sour brine (50,00060,000 ppm of chloride ion and 79-84 ppm of hydrogen sul fide) was passed into the cell through feed line 68 and was removed from the cell through line 69. The water flow rate, amperage, and voltage drop between the electrodes were measured and, in addition, water samples were collected from the lines 68 and 69 and the pH and hydrogen sulfide concentrations determined. Pertinent data relating to these tests are set forth in Table -l which follows:

TABLE 1 Run No. l 2 3 Amperage 200 Voltage 4.2 4.2 4.4 Water rate (gal/min) 5.44 7.29 10.2 Before electrolysis H 8 (ppm) 84 83 79 pH 6.5 6.]4 6.57 Immediately after discharge from cell (1 minute) H S (ppm) 74 67 66 pH 6.2 5.80 6.17 5 minutes after electrolysis H 8 (ppm) 46 56 56 H 6.37 5.90 6.25 30 minutes after electrolysis H 5 (ppm) 43 53 56 H 6.37 5.86 6.23 l hour after electrolysis H 8 (ppm) 43 53 56 pH 6.37 5.86 6.23 2 hours after electrolysis H S (ppm) 42 53 57 pH 6.37 5.86 6.23

These data indicate that a substantial reduction of the hydrogen sulfide in the sour brine can be accomplished with electrolysis. Further, the data indicate that the sodium hypochlorite generated in the cell continues 'to react with the hydrogen sulfide in the brine after the treated brine is removed from the cell.

EXAMPLE II The cell shown in FIG. 2, previously employed in Example I, was modified so that the sour brine was introduced into the cell through four equally spaced /2 inch [.D. valved inlet lines fed from an inlet manifold rather than through the single inlet line previously utilized. This modification was made to prevent plugging experienced at the previously employed low flow rates and to reduce anode erosion. Sour brine was passed through the cell at rates of from 360 to 600 bpd (i.e., barrels per day) and the brine analyzed before and after treatment for hydrogen sulfide content. Pertinent details relating to these runs are set forth in Table 2 which follows:

ITABLEZ Weight of Anode (Saturated with Water-33.75 lbs) Discharge Removal Inlet RH" No. Rate. Bl'l) H15. ppm H25, ppm H S, ppm Amps Volts 1* 600 94 76 18 315 5.7 t 2* 600 98 67 31 325 5.8 3 600 98 75 23 320 5.8 4 600 97 8O 17 315 5.8 5 400 97 72 25 320 5.9 6 400 96 72 24 315 5.8 7 300 103 68 35 300 6.0 8 400 108 88 20 200 4.4 9 400 l 10 83 27 190 4.4 10 400 96 78 18 180 4.4 l l 360 94 76 I8 190 4.6 12 600 NR NR NR 180 4.6 13 600 91 76 180 4.4 14 600 NR NR NR 180 4.6 15 600 95 82 13 170 4.6

The above data reveal that in the single pass a substantial reduction of the hydrogen sulfide content of the sour brine can be accomplished. By treating the sour brine in cells operated in series any desired reduction in sulfide concentration can be satisfactorily achieved.

EXAMPLE lll Using a 10 cell (series connected) commercially available hypochlorite cell unit operated at 5,000 amperes with a 46-50 volt potential across the cells (4.65.O volts potential per cell) and utilizing a processing scheme in which the incoming contaminated rately in cells employing make-up water to which sodium chloride has been added and the effluent therefrom having a relatively high concentration of sodium hypochlorite can be introduced into the sour brine stream where the hypochlorite reacts with the eliminates the hydrogen sulfide.

What is claimed is:

l. A process for recovering fluid hydrocarbons from subterranean formation penetrated by an injection well and a production well which comprises:

a. injecting brine into said formation through the injection well, b. forcing the said brine toward said production well,

brine was recycled through the cell bank in the manner I awing a mixture of the liquid hydrocarbon shown in FIG. 1, it was found that the hydrogen sulfide n brine contammg hydrogen sulfide from said content of the brine leaving the recycle tank (see FIG. P P":

1, line 22 could be reduced to as low as 0 ppm of hy- Separatmg sald llquld hydrocarbon from the y drogen s lfid 40 gen sulfide containing brine,

Pertinent details relating to this series of runs are set 6. subjecting the hydrogen sulfide containing brine to forth in Table 3 which follows. electrolysis to form sodium hypochlorite whereby TABLE 3 1 H 8 NaOH Influent Tank Efliuent removed addition from Flow rate rate H28 H28 NaOCl stream (bblslday) (lbs/day) (p.p.m.) pH (p.p.m.) (p.p.m.) pH (lbs/day) Assumed infiuent to contain p.p.m. H S.

A variety Of cells are described in the art for preparreaction with the said hydrogen sulfide yields brine mg Sodium hypochlorite Such as, for p those with a substantially reduced hydrogen sulfide con-' shown in US. Pat. Nos. 1.996.769, 1,609,757, tent,

1.609158, 2,385,903 and 3.222.269. Preferably, the f. Separating insolubles from the treated brine and cell or cells employed Wlll be of the enclosed type to 65 reinjecting the thusmeated brine into the said prevent escape of hydrogen sulfide to the atmosphere prior to reaction with the formed sodium hypochlorite.

A number of different cell arrangements can be utilized in this invention. For example, the sour brine can be sent through a bank of series operated cells and, if desired, the sodium hypochlorite can be prepared sepajection well. 2. The process of claim 1 wherein the concentration of the hydrogen sulfide-containing brine being electrolyzed in step (e) is from about 2 to about 500 parts per million. 

2. The process of claim 1 wherein the concentration of the hydrogen sulfide-containing brine being electrolyzed in step (e) is from about 2 to about 500 parts per million. 